Method for reducing the viscosity of viscous fluids

ABSTRACT

A viscous fluid, such as heavy crude oil which is too viscous to enable it to be pumped from a flowing phase of a reservoir into and along a pipeline for delivery to a refinery or other storage facility, may be contacted with a formulation to reduce its viscosity. The formulation comprises a polymeric material AA which includes —O— moieties pendent form a polymeric backbone thereof and said material is optionally cross-linked. In one embodiment, the formulation may comprise polyvinyl alcohol. In an alternative embodiment, the formulation may comprise a cross-linked polymeric material, such as cross-linked polyvinyl alcohol. After the viscous composition has been transported to a desired location, it may be separated from the other components.

This application is the U.S. National Phase of International ApplicationPCT/GB2004/004083, filed 27 Sep. 2004, which designated the U.S.PCT/GB2004/004083 claims priority to British Application No. 0323067.9filed 2 Oct. 2003 and 0404051.5 filed 24 Feb. 2004. The entire contentof these applications are incorporated herein by reference.

This invention relates to viscous fluids and particularly, although notexclusively, relates to the reduction of the viscosity of viscous fluidsto facilitate their flow between two locations. Preferred embodimentsrelate to the reduction of the viscosity of viscous petroleum tofacilitate its transport between a place where it is produced and apoint downstream thereof.

There are many known petroleum-containing formations from which verylittle petroleum can be obtained by normal production techniques becausethe petroleum viscosity is so high that the petroleum will not flow atformation conditions even if a substantial pressure differential, eithernatural or artificially induced as by injecting water or other fluidsinto the formation, is applied to the petroleum. These petroleumformations are sometimes referred to as heavy oil formations, and forthe purpose of this disclosure, by heavy oil or viscous petroleum it ismeant crude petroleum having an API gravity less than about 25° API at75° F.

Various techniques have been disclosed for stimulating the recovery ofviscous petroleum or heavy oil and facilitating its transport alongpipelines from a production facility to a refinery. However, there stillexists a problem, especially where the petroleum is extremely viscoussuch as that found in heavy oil reservoirs or tar sand deposits.

It is an object of the present invention to address problems associatedwith the flow and/or transport of viscous fluids.

According to a first aspect of the invention, there is provided a methodof reducing the viscosity of a viscous composition which is arranged toflow along a fluid flow path, said method comprising contacting theviscous composition with a treatment fluid formulation, said treatmentfluid formulation comprising a polymeric material AA which includes —O—moieties pendent from a polymeric backbone thereof, wherein polymericmaterial AA is optionally cross-linked.

The ratio of the viscosity of the viscous composition immediately priorto contact with the treatment fluid formulation to the viscosity aftercontact with the treatment fluid formulation is preferably at least 1.2,more preferably at least 1.5.

The viscosity of the viscous composition after contact with thetreatment fluid formulation is preferably less than 300 cP, morepreferably less than 200 cP, especially less than 100 cP measured at 25°C. and 1000 s⁻¹ more preferably when measured at 100 s⁻¹.

The viscosity of the viscous composition after contact with thetreatment fluid formulation is preferably less than 4000 cP for allshear rates in the range 20-1000 s⁻¹.

The viscous composition after contact with the treatment fluidformulation preferably exhibits shear thinning—i.e. the viscositypreferably falls as the shear rate increases. This may advantageouslyimprove the mobility of the viscous composition. Said viscouscomposition may exhibit shear thinning as aforesaid at least over theshear rate range 0.1 to 100 s⁻¹. The shear thinning property mayfacilitate the re-commencement of flow of the viscous composition afterflow in the fluid path has been stopped, for any reason. Advantageously,even if the viscous composition separates from parts of the treatmentfluid formulation, for example during suspension of flow along the fluidflow path, on commencement of flow, the viscous composition andtreatment fluid formulation may again become intimately mixed and theviscosity may be reduced as described.

The method may be used to reduce the viscosity of many types of viscouscompositions provided that the viscous compositions can be caused toform a dispersion when contacted with said treatment fluid formulation.Said viscous composition is preferably organic. It is preferably aviscous fluid. It is preferably an oil. It preferably comprisespetroleum. It preferably comprises a viscous petroleum.

Said viscous composition may be derived from a heavy oil reservoirand/or from tar sand deposits. It may be derived from a deep wellwherein the composition may be sufficiently warm down the well to enableit to flow; but the viscosity rises as the composition is withdrawn fromthe well (and cools) making it more difficult to flow.

Said treatment fluid formulation preferably comprises a hydrogel.

Said treatment fluid formulation is preferably not injected into aninjection well of a subterranean formation in order to contact saidviscous composition.

Said treatment fluid formulation is preferably initially contacted withsaid viscous composition at or downstream of a production means, forexample at or downstream of a producing face of a subterraneanformation. In one embodiment, said treatment fluid formulation may beinitially contacted with said viscous composition below ground (forexample at or adjacent to a producing face of a subterranean formation)to reduce the viscosity of said viscous composition below ground andfacilitate its transport to the surface. In another embodiment, saidtreatment fluid formulation may be contacted with said viscouscomposition at or adjacent the surface of the ground after the viscouscomposition has been transported to the surface, for example using heavypumps.

Said treatment fluid formulation is preferably not used to drive theviscous composition through a subterranean formation.

Said fluid flow path is preferably defined by a conduit means.

Said conduit means preferably includes a first conduit part (e.g. apipeline) which is arranged downstream of a production means, preferablyabove ground level. Said first conduit part preferably contains saidviscous composition after contact with the treatment fluid formulation.

Said first conduit part may be circular in cross-section. Said part mayhave a cross-sectional area for at least part of its length of at least5 cm, preferably at least 10 cm. In some cases, the cross-section mayhave a diameter of up to 0.5 m. Said first conduit part preferablyextends away from a position where the viscous composition is produced,suitably in a transverse direction to the vertical. Said first conduitpart may have a length of at least 5 m, preferably at least 20 m,especially at least 100 m. In some cases, said first conduit part mayhave a length of more than 1,000 m, more than 5,000 m, more than 10,000m, even more than 500 km. Long pipes may be arranged to deliverpetroleum to a refinery; such pipes may extend partly above and partlybelow ground.

Said fluid flow path (e.g. said conduit means) may extend between afirst point, remote from the point of production of the viscouscomposition, and a second point closer to, for example at or adjacentto, the point of production of the viscous composition. Said first pointmay be above ground and may be, for example, a refinery; said secondpoint may be closer to the producing face of a subterranean formation.It may be at or adjacent to the producing face.

Said fluid flow path may be defined, in part, by a second conduit partwhich extends upwardly from below ground to above ground. Said secondconduit part may be a riser pipe. Said second conduit part may containsaid viscous composition after contact with the treatment fluidformulation.

Said treatment fluid formulation is preferably arranged to disperseand/or emulsify said viscous composition on contact therewith. Saidviscous composition may not be substantially particulate prior tocontact with said treatment fluid formulation—it may be in the form of asubstantially homogenous fluidic mass. Preferably, flow along said fluidflow path is turbulent, at least in part, thereby to facilitateformation of said dispersion and/or emulsion. Preferably, flow isturbulent at the point of initial contact of said viscous compositionwith said treatment fluid formulation so that said composition isdispersed and/or emulsified on contact with said formulation.

In the method, a delivery flow path is preferably defined which isarranged to communicate with said fluid flow path wherein said treatmentfluid formulation is dosed into said viscous composition in said fluidflow path via said delivery flow path. Said delivery flow pathpreferably communicates with said fluid flow path at or downstream of aproducing face of the subterranean formation.

The ratio of the flow rate (in weight per unit time) of treatment fluidformulation in said delivery flow path to the flow rate (in the sameunits) of viscous composition in said fluid flow path may be in therange 0.1 to 2.5, preferably in the range 0.2 to 1, more preferably inthe range 0.4 to 0.8, especially in the range 0.6 to 0.7.

The mass fraction of viscous composition in said fluid flow path aftercontact with said treatment fluid formulation is preferably in the range0.4 to 0.8.

Preferably, immediately after contact between said viscous compositionand said treatment fluid formulation, the composition in said fluid flowpath includes 30 to 80 wt % (preferably 40 to 80 wt %, more preferably50 to 70 wt %) of material derived from said viscous composition and 20to 70 wt %, (preferably 20 to 60 wt %, more preferably 30 to 50 wt %,especially 30 to 45 wt %) of material derived from said treatment fluidformulation.

Suitably, immediately after contact between said viscous composition andsaid treatment fluid formulation, the composition in said fluid flowpath includes at least 20 wt %, preferably at least 25 wt %, morepreferably at least 30 wt %, water; and at least 40 wt %, preferably atleast 50 wt %, more preferably at least 55 wt % of said viscouscomposition, especially of oil.

The amount of water in the composition in said fluid flow pathimmediately after contact between said viscous composition and saidtreatment fluid formulation is preferably less than 70 wt %, morepreferably less than 60 wt %, especially less than 50 wt %, morepreferably 40 wt % or less. The amount of water may be in the range 20to 50 wt %.

Said treatment fluid formulation suitably has a viscosity at 25° C. and1000 s⁻¹ of greater than 1 cP, preferably greater than 2 cP. Saidtreatment fluid formulation preferably has a viscosity under theconditions described of not greater than 50 cP, preferably of 10 cP orless.

Said treatment fluid formulation is preferably aqueous. It may includeat least 70 wt %, preferably at least 80 wt %, more preferably at least90 wt %, especially at least 95 wt % water. The amount of water may beless than 99.6 wt %. Said treatment fluid formulation preferablyincludes 90 to 99.6 wt % water.

Said treatment fluid formulation suitably includes at least 0.2 wt %,preferably at least 0.4 wt %, especially at least 0.5 wt % of saidpolymeric material AA. Said formulation preferably includes less than 10wt %, more preferably less than 8 wt %, especially less than 5.5 wt % ofsaid polymeric material AA.

In a preferred embodiment, said treatment fluid formulation includes94.5 to 99.6 wt % water and 0.4 to 5.5. wt % of said polymeric materialAA; and the ratio of the wt % of said treatment fluid formulation to thewt % of said viscous composition contacted in the method is in the range0.4 to 0.9.

Water for use in the treatment fluid formulation may be derived from anyconvenient source. It may be potable water, surface water, sea water,aquifer water, deionised production water and filtered water derivedfrom any of the aforementioned sources. The water may be treated so thatit is suitable for use in the method. For example, it may be treated byaddition of oxygen scavengers, biocides, corrosion inhibitors, scaleinhibitors, anti-foaming agents and flow improvers. Sea water and/orwater from other sources may be deoxygenated and/or desulphonated.

Said polymeric material AA is preferably soluble in water at 25° C.Preferably, when said polymeric material AA is not cross-linked,polymeric material AA in said treatment fluid formulation is wholly orpartially dissolved therein to define a solution or dispersion.

Whilst the applicant does not wish to be bound by any theory, saidoptionally cross-linked polymeric material AA may be arranged to coatparticles of the viscous composition, whereby the coated particles maythen be more easily dispersed compared to uncoated particles such asoil. Said polymeric material AA may be arranged to be absorbed onto theviscous composition, for example oil, to enable said particles to form.Said polymeric material AA is preferably not a conventional surfactanthaving a hydrophobic portion, for example a hydrophobic tail and ahydrophilic portion, for example an ionic head. Thus, it is believedthat formation of said coated particles preferably does not involve ahydrophobic tail part interacting with, for example oil, and ahydrophilic part interacting with, for example water. According to theapplicant's theory, the polymeric material AA may form “balls” made upof “threads” of the polymeric material. It is believed that amultiplicity of such balls associate with the surface of oil dropletsformed in the method, to surround the droplets and thereby stabilisethem. When the polymeric material AA is cross-linked the cross-links mayformalise the shape of the balls and make them robust.

Said polymeric backbone of polymeric material AA preferably includescarbon atoms. Said carbon atoms are preferably part of —CH₂— moieties.Preferably, a repeat unit of said polymeric backbone includes carbon tocarbon bonds, preferably C—C single bonds. Preferably, said polymericmaterial AA includes a repeat unit which includes a —CH₂— moiety.Preferably, said polymeric backbone does not include any —O— moieties,for examples —C—O— moieties such as are found in an alkyleneoxy polymer,such as polyethyleneglycol. Said polymeric backbone is preferably notdefined by an aromatic moiety such as a phenyl moiety such as is foundin polyethersulphones. Said polymeric backbone preferably does notinclude any —S— moieties. Said polymeric backbone preferably does notinclude any nitrogen atoms. Said polymeric backbone preferably consistsessentially of carbon atoms, preferably in the form of C—C single bonds.

Said treatment fluid formulation may include a hydrogel which may be anoptionally cross-linked polysaccharide, polyvinylalcohol orpolyvinylacetate.

Said —O— moieties are preferably directly bonded to the polymericbackbone.

Said polymeric material AA preferably includes, on average, at least 10,more preferably at least 50, —O— moieties pendent from the polymericbackbone thereof.

Said —O— moieties are preferably a part of a repeat unit of saidpolymeric material AA.

Preferably, said —O— moieties are directly bonded to a carbon atom insaid polymeric backbone of polymeric material AA, suitably so that saidpolymeric material AA includes a moiety (which is preferably part of arepeat unit) of formula:

where G¹ and G² are other parts of the polymeric backbone and G³ isanother moiety pendent from the polymeric backbone. Preferably, G³represents a hydrogen atom.

Preferably, said polymeric material AA includes a moiety

Said moiety III is preferably part of a repeat unit. Said moiety III maybe part of a copolymer which includes a repeat unit which includes amoiety of a different type compared to moiety III. Suitably, at least 60mole %, preferably at least 80 mole %, more preferably at least 90 mole% of polymeric material AA comprises repeat units which comprise(preferably consists of) moieties III. Preferably, said polymericmaterial AA consists essentially of repeat units which comprise(preferably consist of) moieties III.

Suitably, 60 mole %, preferably 80 mole %, more preferably 90 mole %,especially substantially all of said polymeric material AA comprisesvinyl moieties which are optionally cross-linked.

Preferably, the free bond to the oxygen atom in the —O— moiety pendentfrom the polymeric backbone of polymeric material AA (and preferablyalso in moieties II and III) is bonded to a group R¹⁰ (so that themoiety pendent from the polymeric backbone of polymeric material AA isof formula —O—R¹⁰). Preferably group R¹⁰ comprises fewer than 10, morepreferably fewer than 5, especially 3 or fewer carbon atoms. Itpreferably only includes atoms selected from carbon, hydrogen and oxygenatoms. R¹⁰ is preferably selected from a hydrogen atom and analkylcarbonyl, especially a methylcarbonyl group. Preferably moiety —O—R¹⁰ in said polymeric material AA is an hydroxyl or acetate group.

Said polymeric material AA may include a plurality, preferably amultiplicity, of functional groups (which incorporate the —O— moietiesdescribed) selected from hydroxyl and acetate groups. Said polymericmaterial AA preferably includes a multiplicity of hydroxyl groupspendent from said polymeric backbone. Said polymeric material AApreferably includes a multiplicity of acetate groups pendent from thepolymeric backbone.

Preferably, each free bond to the oxygen atoms in —O— moieties pendentfrom the polymeric backbone in polymeric material AA, except for anyfree bonds which are involved in cross-linking the polymeric materialAA, is of formula —O—R¹⁰ wherein each group —OR¹⁰ is selected fromhydroxyl and acetate.

Preferably, said polymeric material AA includes a vinyl alcohol moiety,especially a vinyl alcohol repeat unit. Said polymeric material AApreferably includes a vinyl acetate moiety, especially a vinylacetaterepeat unit. Polyvinylalcohol is generally made by hydrolysis ofpolyvinylacetate. Said polymeric material AA may comprise a 0-100%hydrolysed, preferably a 5 to 95% hydrolysed, more preferably a 60 to 90wt %, especially a 70 to 85 wt % hydrolysed polyvinylacetate

Said polymeric material AA may have a number average molecular weight(Mn) of at least 10,000, preferably at least 50,000, especially at least75,000. Mn may be less than 500,000, preferably less than 400,000. Saidpolymeric material AA is preferably a polyvinyl polymer. Said polymericmaterial AA may be a copolymer.

Said polymeric material AA is preferably a polyvinyl alcohol polymer orcopolymer.

Preferably, said polymeric material AA includes at least one vinylalcohol/vinyl acetate copolymer which may include greater than 5%,suitably includes greater than 30 wt %, preferably greater than 65%,more preferably greater than 80 wt % of vinyl alcohol moieties.

Said polymeric material AA may be a random or block copolymer.

As described above, polymeric material AA is optionally cross-linked. Across-linked material may be used in the method when the chemical orphysical conditions to which the treatment fluid formulation may besubjected during the reduction in viscosity of the viscous compositionand/or during flow in a conduit means, for example in said first conduitpart (when provided) as described above, may be relatively harsh. Inmany applications, it is not be necessary to cross-link polymericmaterial AA.

A cross-linked material as described is preferably a hydrogel. Such ahydrogel may be selected from a cross-linked natural or syntheticpolysaccharide, polyvinylalcohol or polyvinylacetate.

When a cross-linked material is used in the method, said methodpreferably comprises selecting a said polymeric material AA; selecting amaterial BB which includes a functional group which is able to react inthe presence of is said polymeric material AA to cross-link polymericmaterial AA and form a polymeric material CC; and causing the formationof said polymeric material CC by a reaction involving said polymericmaterial AA and material BB.

The ratio of the wt % of said material BB to the wt % of said polymericmaterial AA selected for preparation of said polymeric material CC issuitably less than 0.15, preferably less than 0.10, more preferably lessthan 0.05, especially less than 0.035. Said ratio may be at least 0.005,preferably at least 0.01, more preferably at least 0.015, especially atleast 0.02.

The sum of the wt % of the polymeric material AA and material BBselected for preparation of said polymeric material CC may be at least0.4 wt %. The sum may be less than 5 wt %, preferably less than 4 wt %,more preferably less than 3 wt %, especially less than 2.5 wt %.

Suitably, the amounts of “polymeric material AA” and “material BB”described refer to the sum of the amounts of polymeric materials AA (ifmore than one type is provided) and the sum of the amounts of materialsBB (if more than one type is provided).

Preferably, formation of said polymeric material CC from said polymericmaterial AA and material BB involves a condensation reaction.Preferably, formation of said polymeric material CC involves an acidcatalysed reaction. Preferably, said polymeric material AA and materialBB include functional groups which are arranged to react, for example toundergo a condensation reaction, thereby to form said polymeric materialCC. Preferably, said polymeric material AA and material BB includefunctional groups which are arranged to react for example to undergo anacid catalysted reaction thereby to form said polymeric material CC.

Said material BB may be an aldehyde, carboxylic acid, urea, acroleine,isocyanate, vinyl sulphate or vinyl chloride of a diacid or include anyfunctional group capable of condensing with one or more groups on saidpolymeric material AA. Examples of the aforementioned includeformaldehyde, acetaldehyde, glyoxal and glutaraldehyde, as well asmaleic acid, oxalic acid, dimethylurea, polyacroleines, diisocyanates,divinyl sulphate and the chlorides of diacids.

Said material BB is preferably an aldehyde containing or generatingcompound. Preferably, material BB is an aldehyde containing compound.

Material BB may include one or more aldehyde groups. Whilst it could bea monoaldehyde such as formaldehyde it preferably includes a pluralityof aldehyde groups.

Material BB may have a general formula

where G⁵ represents a direct link or a linking moiety.

G⁵ may be arranged to space apart the —CHO groups thereby to affect thespacing of the cross-linking of polymeric material AA.

In one embodiment, group G⁵ may be a —(CH₂)_(y)— moiety wherein yrepresents 0 to 8, and one or more of the H atoms may be replaced by(but preferably are not replaced by) another atom or group. Preferably,y represents 0 to 6, more preferably 0 to 4, especially 0 to 2.

Group G⁵ may be arranged to introduce some rigidity into thecross-linking of polymeric material AA. For example, group G⁵ mayinclude at least some covalent bonds which are not freely rotatable. Forexample, group G⁵ preferably does not consist exclusively of a —CH₂—chain wherein each carbon-carbon bond will be freely rotatable butpreferably includes an atom or group or other means which restricts freerotation compared to a case wherein G⁵ consists of a —CH₂— chain. Forexample G⁵ may incorporate bulky atoms or groups; and/or unsaturatedatoms or groups; and/or atoms or groups which hinder free rotation dueto electronic effects.

Group G⁵ may include at least 1, preferably at least 2, more preferablyat least 3, especially at least 4, carbon atoms in a chain extendingbetween the two —CHO groups.

In one embodiment, group G⁵ incorporates one or more aromatic orheteroaromatic groups. Such groups may be arranged to restrict rotationas described. Preferred heteroaromatic groups include N-containingheteroaromatic groups. Preferred aromatic and heteroaromatic groups areselected from optionally-substituted phenyl and N-containing aromaticgroups, such as pyridinyl groups.

Group G⁵ preferably includes both an aromatic and N-containingheteroaromatic group.

Group G⁵ preferably includes some charge separation. It preferablyincludes a polar group. It preferably includes a cationic group. Apreferred cationic group is one which includes a N⁺ moiety.

Group G⁵ may itself include one or more aldehyde (or other) functionalgroups.

Said polymeric material CC may include a moiety

wherein the free bonds of the oxygen atoms are bonded to the polymericbackbone and the free bond of the carbon atom is bonded to a residue ofthe material BB. The residue of material BB may also be bonded to thepolymeric backbone of another polymeric chain (for example of apolymeric material AA as described), thereby to cross-link polymericmaterial AA.

Said material BB may comprise:

-   (i) a first polymeric material having a repeat unit of formula

wherein A and B are the same or different, are selected fromoptionally-substituted aromatic and heteroaromatic groups and at leastone comprises a relatively polar atom or group and R¹ and R²independently comprise relatively non-polar atoms or groups; or

-   (ii) a first polymeric material prepared or preparable by providing    a compound of general formula

wherein A, B, R¹ and R² are as described above, in an aqueous solventand causing the groups C═C in said compound to react with one another toform said first polymeric material.

In the first polymeric material described above, A and/or B could bemulti-cyclic aromatic or heteroaromatic groups. Preferably, A and B areindependently selected from optionally-substituted five or morepreferably six-membered aromatic and heteroaromatic groups. Preferredheteroatoms of said heteroaromatic groups include nitrogen, oxygen andsulphur atoms of which oxygen and especially nitrogen, are preferred.Preferred heteroaromatic groups include only one heteroatom. Preferably,a or said heteroatom is positioned furthest away from the position ofattachment of the heteroaromatic group to the polymer backbone. Forexample, where the heteroaromatic group comprises a six-membered ring,the heteroatom is preferably provided at the 4-position relative to theposition of the bond of the ring with the polymeric backbone.

Preferably, A and B represent different groups. Preferably, one of A orB represents an optionally-substituted aromatic group and the other onerepresents an optionally-substituted heteroaromatic group. Preferably Arepresents an optionally-substituted aromatic group and B represents anoptionally-substituted heteroaromatic group especially one including anitrogen heteroatom such as a pyridinyl group.

Unless otherwise stated, optionally-substituted groups described herein,for example groups A and B, may be substituted by halogen atoms, andoptionally substituted alkyl, acyl, acetal, hemiacetal, acetalalkyloxy,hemiacetalalkyloxy, nitro, cyano, alkoxy, hydroxy, amino, alkylamino,sulphinyl, alkylsulphinyl, sulphonyl, alkylsulphonyl, sulphonate, amido,alkylamido, alkylcarbonyl, alkoxycarbonyl, halocarbonyl and haloalkylgroups. Preferably, up to 3, more preferably up to 1 optionalsubstituents may be provided on an optionally substituted group.

Unless otherwise stated, an alkyl group may have up to 10, preferably upto 6, more preferably up to 4 carbon atoms, with methyl and ethyl groupsbeing especially preferred.

Preferably, A and B each represent polar atoms or group—that is, thereis preferably some charge separation in groups A and B and/or groups Aand B do not include carbon and hydrogen atoms only.

Preferably, at least one of A or B includes a functional group which canundergo a condensation reaction, for example on reaction with saidpolymeric material AA. Preferably, A includes a said functional groupwhich can undergo a condensation reaction.

Preferably, one of groups A and B includes an optional substituent whichincludes a carbonyl or acetal group with a formyl group being especiallypreferred. The other one of groups A and B may include an optionalsubstituent which is an alkyl group, with an optionally substituted,preferably unsubstituted, C₁₋₄ alkyl group, for example a methyl group,being especially preferred.

Preferably, A represents a group, for example an aromatic group,especially a phenyl group, substituted (preferably at the 4-positionrelative to polymeric backbone when A represents anoptionally-substituted phenyl group) by a formyl group or a group ofgeneral formula

where x is an integer from 1 to 6 and each R³ is independently an alkylor phenyl group or together form an alkalene group.

Preferably, B represents an optionally-substituted heteroaromatic group,especially a nitrogen-containing heteraromatic group, substituted on theheteroatom with a hydrogen atom or an alkyl or aralkyl group. Morepreferably, B represents a group of general formula

wherein R⁴ represents a hydrogen atom or an alkyl or aralkyl group, R⁵represents a hydrogen atom or an alkyl group and X⁻ represents astrongly acidic ion;

Preferably, R¹ and R² are independently selected from a hydrogen atom oran optionally-substituted, preferably unsubstituted, alkyl group.Preferably, R¹ and R² represent the same atom or group. Preferably, R¹and R² represent a hydrogen atom.

Preferred first polymeric materials may be prepared from any of thecompounds described on page 3 line 8 to line 39 of GB2030575B by themethod described in WO98/12239 and the contents of the aforementioneddocuments are incorporated herein by reference.

Said first polymeric material may be of formula

wherein A, B, R¹ and R² are as described above and n is an integer.Integer n is suitably 10 or less, preferably 8 or less, more preferably6 or less, especially 5 or less. Integer n is suitably at least 1,preferably at least 2, more preferably at least 3.

Said polymeric material CC suitably includes a moiety of formula

wherein R¹, R² and B are as described above, A¹ represents a residue ofgroup A described above after the reaction involving said firstpolymeric material and polymeric material AA, Y represents a residue ofsaid polymeric material AA after said reaction involving said firstpolymeric material and polymeric material AA and X represents a linkingatom or group extending between the residues of said first polymericmaterial and said polymeric material AA. In one preferred embodiment A¹represents an optionally-substituted phenyl group, X represents a group

which is bonded via the oxygen atoms to a residue of said polymericmaterial AA. For example, group X may be bonded to the polymericbackbone of said polymeric material AA.

When said treatment fluid formulation comprises a polymeric material AAwhich is cross-linked, preferably, prior to the treatment fluidformulation contacting the viscous composition, it has attained at least70% of the maximum viscosity attainable for the formulation at thetemperature at which it is to contact the viscous composition.Preferably, it has attained at least 80%, more preferably 90%,especially about 100% of its maximum viscosity. Thus, in an especiallypreferred embodiment, said polymeric material AA and material BB aresubstantially completely reacted to form said polymeric material CCprior to contact with said viscous composition.

After the viscous composition has been delivered to a desired location(for example a refinery) the viscous composition may be caused toseparate from other components of the treatment fluid formulation. Thismay be achieved by simply reducing any mixing or turbulent movement ofthe mixture and allowing the viscous composition to settle out from thewater and optionally cross-linked polymeric material AA (which may besubstantially soluble in the water under the conditions of settling).The rate of setting may be increased by increasing the temperature ofthe viscous composition. Additionally, the viscous composition may bediluted with light oil or mechanical means may be used to encouragesettling. In some cases, for example, when said polymeric material AA iscross-linked, it may settle out as described. In other cases, whereinpolymeric material AA is cross-linked, the method of the first aspectmay include the step of contacting the mixture with a breaker meansarranged to break an aqueous emulsion of the viscous composition. Whenpolymeric material CC comprises 1,2-diol linkages, the breaker means ispreferably arranged to cleave 1,2-diol linkages. Said breaker meanspreferably comprises a periodate (e.g. sodium or potassium periodate) inwater.

The method of the first aspect preferably includes the step ofseparating at least a part of the treatment fluid formulation from theviscous composition after the viscous composition has flowed along saidfluid flow path. After separation, said viscous composition suitablyincludes less than 10 wt %, preferably less than 5 wt %, especially lessthan 2 wt % water. After separation said viscous composition suitablyincludes less than 2 wt %, preferably less than 1 wt %, more preferablyless than 0.5 wt %, especially less than 0.2 wt %, of saidoptionally-cross-linked polymeric material AA.

When the method includes the separating step as described, the treatmentfluid formulation which is separated from the viscous composition may bere-used to reduce the viscosity of further viscous composition. Forexample, the method may involve a continuous or semi-continuous processwherein treatment fluid formulation is contacted with viscouscomposition to reduce its viscosity; the mixture is then caused to flowdownstream along a fluid flow path thereby to deliver the viscouscomposition to a desired location; the viscous composition and treatmentfluid formulation are separated; the viscous composition is used and/orstored as required in said desired location; the treatment fluidformulation is delivered to a location thereby to contact furtherviscous composition upstream of said desired location; and the processis suitably repeated.

According to a second aspect of the present invention there is provideda method of preparing a treatment fluid formulation (e.g. for reducingthe viscosity of a viscous composition) comprising:

-   -   contacting an optionally cross-linked polymeric material AA as        described according to the first aspect with water.

Preferably, the polymeric material AA is dissolved in the water therebyto prepare an aqueous solution of said polymeric material AA.Preferably, the polymeric material AA is in the form of a solid prior tocontact with water.

Preferably, at least 100 liters more preferably at least 1000 liters ofsaid treatment fluid formulation is prepared.

When the treatment fluid formulation is cross-linked, the method maycomprise: selecting a polymeric material AA (for example apolyvinylalcohol) and a material BB as described according to said firstaspect; and

-   causing the formation of a said polymeric material CC by a reaction    involving said polymeric material AA and said material BB.

In the preparation of said polymeric material CC, a catalyst ispreferably provided for catalysing the reaction of the polymericmaterial AA and said material BB. Said catalyst is preferably a proticacid. Said catalyst is preferably phosphoric acid. Advantageously, whenthe fluid flow path of the first aspect is defined by steel pipes thephosphoric acid may facilitate the formation of an anti-corrosive layeron the pipes.

The method is preferably carried out adjacent or close to an oil field,for examples within 1 mile of a production well thereof. The method ispreferably carried out within 1 mile of an oil supply line which isarranged to transport oil between two locations.

According to a third aspect of the invention, there is provided atreatment fluid formulation comprising:

-   -   at least 95 wt % water    -   4 wt % or less of said polymeric material AA which has        optionally been cross-linked as described above.

According to a fourth aspect of the invention, there is provided amethod of reducing the viscosity of a viscous composition which isarranged to flow along a fluid flow path, said method comprisingcontacting the viscous composition with a treatment fluid formulation,wherein said treatment fluid formulation includes a polymeric materialwhich:

-   (a) is arranged to associate with, for example absorb onto, said    viscous composition, especially oil, in order to enable droplets of    said viscous composition to be formed, and/or stablised; and/or-   (b) is arranged to form a coating (which may be discontinuous)    around droplets of said viscous composition;-   (c) is arranged to form a hydrogel which is able to stabilise    droplets of said viscous composition, especially oil.

Preferably, said polymeric material in said treatment fluid formulation(which is preferably optionally cross-linked polymeric material AAdescribed above) is arranged to form a material, for example a hydrogelwhich is arranged to associate with, for example coat, droplets of saidviscous composition, especially oil, in order to enable the formulationof a dispersion comprising said droplets.

Preferably, said polymeric material has each of the effects described in(a), (b) and (c) of the fourth aspect.

According to a fifth aspect of the invention, there is provided a methodof reducing the viscosity of a viscous composition which is arranged toflow along a fluid flow path, said method comprising contacting theviscous composition with a treatment fluid formulation which includes ahydrogel, for example of an optionally cross-linked polymeric materialAA as described herein.

The invention extends to a receptacle containing at least 100 liters,preferably at least 200 liters, especially at least 1000 liters of asaid treatment fluid formulation as described herein.

According to a sixth aspect of the invention, there is provided a fluidflow path, for example a conduit means (preferably having across-sectional diameter at least in part of at least 5 cm and a lengthof at least 5 m) which contains a fluid comprising petroleum, water andan optionally cross-linked polymeric material AA as described herein.Said polymeric material may be a hydrogel, preferably as describedherein.

Any feature of any aspect of any invention or embodiment describedherein may be combined with any feature of any aspect of any otherinvention or embodiment described herein mutatis mutandis.

Specific embodiments of the invention will now be described, by way ofexample, with reference to FIG. 1 which is a plot of viscosity vs. shearrate for various formulations.

In general terms, heavy crude oil (and associated material) which may betoo viscous to enable it to be pumped from the flowing face of areservoir into and along a pipeline, for example to a refinery or otherstorage facility, may be contacted with a formulation at any point whereit is desirable to reduce the oil viscosity. In a first embodiment, theformulation may comprise polyvinyl alcohol which alone has been found tobe capable advantageously of reducing the viscosity of crude oil therebyenabling it to flow. In a second embodiment, the formulation maycomprise a cross-linked polymeric material, for example cross-linkedpolyvinyl alcohol. The material of the second embodiment may be morerobust compared to that of the first embodiment and may therefore beused in more challenging situations.

After, the oil has been transported to a desired location it may beseparated from the other components in the mixture by allowing it tosettle; by increasing its temperature; by dilution with light oil; bymechanical separation such as centrifugation (or the like); or bytreatment with a chemical means such as a breaker which is arranged tobreak down cross-linked polymeric material.

Further details on the process are provided below.

EXAMPLE 1

60 g of an aqueous solution comprising 0.5% by weight polyvinylalcohol(80-95% hydrolyzed) of molecular weight 110,000 was added to ascrew-capped glass vessel. To this was added 40 g of a crude oil whichhad a viscosity between 5800 cP and 6500 cP at a shear rate of 1reciprocal second. The glass vessel was capped and the mixture wasagitated by hand-shaking for approximately 30 seconds.

The viscosity of the subsequent mixture was determined to be between1200 cP and 1800 cP at a shear rate of 1 reciprocal second and less than200 cP at 100 s⁻¹.

EXAMPLE 2

The procedure described in example 1 was followed with the exceptionthat mixing was performed under high shear. The viscosity of the finalmixture was observed to be in the range 1200 cP to 1800 cP at a shearrate of 1 reciprocal second and less than 200 cP at 100 s⁻¹.

EXAMPLE 3 Preparation of poly(1,4-di(4-(N-methylpyridinyl))-2,3-di(4-(1-formylphenyl)butylidene

This was prepared as described in Example 1 of PCT/GB97/02529, thecontents of which are incorporated herein by reference. In the method,an aqueous solution of greater than 1 wt % of4-(4-formylphenylethenyl)-1-methylpyridinium methosulphonate (SbQ) isprepared by mixing the SbQ with water at ambient temperature. Under suchconditions, the SbQ molecules form aggregates. The solution was thenexposed to ultraviolet light. This results in a photochemical reactionbetween the carbon-carbon double bonds of adjacent4-(4-formylphenylethenyl)-1-methylpyridinium methosulphate molecules (I)in the aggregate, producing a polymer, poly(1,4-di(4-(N-methylpyridinyl))-2,3-di(4-(1-formylphenyl)butylidenemethosulphonate (II).

EXAMPLE 4 Preparation of Poly(vinylalcohol) Solution

A 10 wt % poly(vinylalcohol) solution was prepared by slowly stirring aknown amount of water and adding a known amount of 88% hydrolysedpoly(vinylalcohol) of molecular weight 300,000 to the stirred water. Thesuspension was stirred for 1 hour and, thereafter, the suspension washeated at a temperature of 60° C. until the suspended particlesdissolved and the solution was clear. The solution was then allowed tocool to less than 5° C. and maintained at this temperature until used.

EXAMPLE 5 Preparation of Butylidene Polymer/Poly(vinylalcohol)Formulation

997.5 g of the poly(vinylalcohol) solution prepared in Example 4 and 2.5g of the butylidene polymer prepared in Example 3 were mixed together atambient temperature to give a 10 wt % poly(vinylalcohol)/0.25 wt %butylidene polymer solution. This was diluted down to give a 2 wt %poly(vinyl alcohol)/0.05 wt % butylidene polymer solution. This solutionwas acidified to pH 1.5 with phosphoric acid and left to cure for 1hour. After curing the solution was neutralised using 5M NaOH. Thiscured and neutralised solution was then further diluted to give a 1 wt %poly(vinylalcohol)/0.025 wt % butylidene polymer solution; and a 0.05 wt% polyvinylalcohol/0.0125 wt % butylidene polymer solutions.

On acidification of the polyvinylalcohol/butylidene polymer blend asdescribed, the two polymers react as described in PCT/GB97/02529.

EXAMPLE 6 Protocol for Preparation of Oil Emulsions

Emulsions of oil and the aqueous formulations of Example 5 were preparedat ratios of oil: aqueous formulation of 70:30 and 60:40 with theaqueous phase containing 2 wt %, 1 wt % or 0.5 wt % poly(vinylalcohol).The oil and aqueous formulations were initially mixed using a spatula,then homogenized.

EXAMPLE 7 Protocol for Evaluation of Oil Emulsions

The viscosity against shear rate of the emulsions was measured on 0.65ml samples at 25° C. taking 60 measuring points at 10 second intervalsand a shear rate of 0.1 to 1000 s⁻¹ followed immediately by a rate of1000 to 0.1 s⁻¹. Results are provided in FIG. 1 wherein:

-   -   Lines A and A¹ are comparative examples detailing the results        for two runs undertaken without inclusion of an aqueous        formulation of Example 4.    -   Lines B and B¹ are the results for two runs undertaken using the        aqueous formulation of Example 5 with 2 wt % poly(vinylalcohol).    -   Lines C and C¹ are the results for two runs undertaken using the        aqueous formulation of Example 5 with 1 wt % of        poly(vinylalcohol).    -   Lines D and D¹ are the results for two runs undertaken using the        aqueous formulation of Example 5 with 0.5 wt % of        polyvinylalcohol.

FIG. 1 shows that without the addition of any formulation described inExample 5, the viscosity is relatively high. When the formulation isadded, there is a significant reduction in viscosity.

Thus, the formulation may be dosed into a oil flow at any point at whichit is desired to reduce the oil's viscosity to enable it to betransported. For example, it may be closed in at the bottom of a riserpipe to reduce the viscosity of oil flowing upwardly in the pipe.Alternatively, it may be closed in at or near the surface. Once closedin, the oil may be transported long distances through a pipeline to arefinery or other oil storage facility.

After completion of the transport stage, it is necessary to recover theoil from the emulsion. This may be achieved by allowing the mixture tosettle; by mechanical means or by chemical means. An example of thelatter may involve the addition of 0.1 to 0.3 wt % (preferably about 0.2wt %) of a periodate salt (preferably the sodium salt) to the emulsion.This causes the destruction of the emulsion and enables the oil to berecovered for further processing.

EXAMPLE 8 Preparation of Glutaraldehyde/Poly(vinylalcohol) Formulation

A poly(vinylalcohol) solution of a 88% hydrolysed poly(vinylalcohol)having a molecular weight of about 160,000 is prepared by dissolving 87g of the poly(vinylalcohol) in 1000 ml of water by stirring thecomponents for 24 hours at 80-90° C. The solution is then allowed tocool to 50° C. and 1.29 ml of a 25% solution of glutaraldehyde addedwith stirring for about 1 hour. Then, 100 ml of 1M HCl is added withstirring and a gel forms which may be used as described above.

EXAMPLE 9 Preparation of Glyoxal/Poly(vinylalcohol) Formulation

By a process analogous to Example 8 a glyoxal cross-linkedpoly(vinylalcohol) may be prepared.

The materials of Examples 8 and 9 may be used in viscosity reduction asdescribed herein.

Attention is directed to all papers and documents which are filedconcurrently with or previous to this specification in connection withthis application and which are open to public inspection with thisspecification, and the contents of all such papers and documents areincorporated herein by reference.

All of the features disclosed in this specification (including anyaccompanying claims, abstract and drawings), and/or all of the steps ofany method or process so disclosed, may be combined in any combination,except combinations where at least some of such features and/or stepsare mutually exclusive.

Each feature disclosed in this specification (including any accompanyingclaims, abstract and drawings) may be replaced by alternative featuresserving the same, equivalent or similar purpose, unless expressly statedotherwise. Thus, unless expressly stated otherwise, each featuredisclosed is one example only of a generic series of equivalent orsimilar features.

The invention is not restricted to the details of the foregoingembodiment (s). The invention extends to any novel one, or any novelcombination, of the features disclosed in this specification (includingany accompanying claims, abstract and drawings), or to any novel one, orany novel combination, of the steps of any method or process sodisclosed.

1. A method for reducing the viscosity of a viscous composition which isarranged to flow along a fluid flow path, said method comprisingcontacting the viscous composition in said fluid flow path with atreatment fluid formulation, said treatment fluid formulation comprisinga polymeric material AA which includes —O— moieties pendent from apolymeric backbone thereof, wherein said polymeric material AA comprisespolyvinyl acetate which has been 60 to 95% hydrolyzed to polyvinylalcohol, wherein polymeric material AA is optionally cross-linked andwherein said treatment fluid formulation is initially contacted withsaid viscous composition in said fluid flow path at or downstream of aproducing face of a subterranean formation.
 2. A method according toclaim 1, wherein the viscosity of the viscous composition after contactwith the treatment fluid formulation is less than 300 cP measured at 25°C. and 1000 s⁻¹.
 3. A method according to claim 2, wherein the viscouscomposition, after contact with the treatment fluid formulation,exhibits shear thinning.
 4. A method according to claim 1, wherein saidviscous composition is an oil.
 5. A method according to claim 1, whereinsaid fluid flow path is defined by a conduit means which includes afirst conduit part which is arranged downstream of a production means.6. A method according to claim 1, wherein said fluid flow path extendsbetween a first point, remote from the point of production of theviscous composition, and a second point closer to the point ofproduction of the viscous composition.
 7. A method according to claim 1,wherein said fluid flow path is defined, in part, by a second conduitpart which extends upwardly from below ground to above ground.
 8. Amethod according to claim 1, wherein said treatment fluid formulation isarranged to disperse and/or emulsify said viscous composition on contacttherewith.
 9. A method according to claim 1, wherein flow is turbulentat the point of initial contact of said viscous composition with saidtreatment fluid formulation so that said composition is dispersed and/oremulsified on contact with said formulation.
 10. A method according toclaim 1, wherein a delivery flow path is defined which is arranged tocommunicate with said fluid flow path wherein said treatment fluidformulation is dosed into said viscous composition in said fluid flowpath via said delivery flow path.
 11. A method according to claim 10,wherein the ratio of the flow rate (in weight per unit time) oftreatment fluid formulation in said delivery flow path to the flow rate(in the same units) of viscous composition in said fluid flow path is inthe range 0.1 to 2.5.
 12. A method according to claim 11, wherein theamount of water in the composition in said fluid flow path immediatelyafter contact between said viscous composition and said treatment fluidformulation is less than 70 wt %.
 13. A method according to claim 1,wherein said treatment fluid formulation has a viscosity at 25° C. and1000 s⁻¹ of greater than 1 cP and not greater than 50 cP.
 14. A methodaccording to claim 1, wherein said treatment fluid formulation includesat least 70 wt % water.
 15. A method according to claim 14, wherein saidtreatment fluid formulation includes at least 0.2 wt % and less than 10wt % of said polymeric material AA.
 16. A method according to claim 1,wherein said treatment fluid formulation includes 94.5 to 99.6 wt %water and 0.4 to 5.5 wt % of said polymeric material AA; and the ratioof the wt % of said treatment fluid formulation to the wt % of saidviscous composition contacted in the method is in the range 0.4 to 0.9.17. A method according to claim 1, wherein said polymeric material AA iswholly soluble in water at 25° C.
 18. A method according to claim 1,wherein said polymeric backbone of said polymeric material AA includescarbon atoms which are part of —CH₂— moieties.
 19. A method according toclaim 2, wherein said polymeric backbone consists essentially of carbonatoms in the form of C—C single bonds.
 20. A method according to claim4, wherein said polymeric material AA includes, on average, at least 10—O— moieties pendent from the polymeric backbone thereof.
 21. A methodaccording to claim 1, which involves selecting a said polymeric materialAA; selecting a material BB which includes a functional group which isable to react in the presence of said polymeric material AA tocross-link polymeric material AA and form a polymeric material CC; andcausing the formation of said polymeric material CC by a reactioninvolving said polymeric material AA and material BB.
 22. A methodaccording to claim 21, wherein material BB has a general formula:

where G⁵ represents a direct link or a linking moiety.
 23. A methodaccording to claim 21, wherein said material BB comprises: (i) a firstpolymeric material having a repeat unit of formula

wherein A and B are the same or different, are selected fromoptionally-substituted aromatic and heteroaromatic groups and at leastone comprises a relatively polar atom or group and R¹ and R²independently comprise relatively non-polar atoms or groups; or (ii) afirst polymeric material prepared or preparable by providing a compoundof general formula

wherein A, B, R¹ and R² are as described above, in an aqueous solventand causing the groups C═C in said compound to react with one another toform said first polymeric material.
 24. A method according to claim 4,wherein after the viscous composition has been delivered to a desiredlocation the viscous composition is caused to separate from othercomponents of the treatment fluid formulation.
 25. A method according toclaim 24, wherein separation is achieved by reducing mixing or turbulentmovement of the mixture and allowing the viscous composition to settleout from the water and optionally cross-linked polymeric material AA.26. A method of reducing the viscosity of a viscous petroleum which isarranged to flow along a fluid flow path, said method comprisingcontacting the viscous petroleum with a treatment fluid formulation,wherein: a delivery flow path is defined which is arranged tocommunicate with said fluid flow path, said treatment fluid formulationbeing dosed into said viscous petroleum in said fluid flow path via saiddelivery flow path; the treatment fluid formulation is initiallycontacted with said viscous composition in said fluid flow path at ordownstream of a producing face of a subterranean formation; the ratio ofthe flow ratio (in weight per unit time) of treatment fluid formulationin said delivery flow path to the flow rate (in the same weight per unittime units) of viscous petroleum in said fluid flow path is in the range0.1 to 2.5; said treatment fluid formulation includes at least 90 wt %water and at least 0.2 wt % of a polymeric material AA; said polymericmaterial AA comprises polyvinyl acetate which has been 60 to 100%hydrolyzed to polyvinyl alcohol.
 27. A method according to claim 26,wherein: said ratio of said flow rates is in the range 0.2 to 1; saidtreatment fluid formulation includes at least 0.5 wt % and less than 5.5wt % of said polymeric material AA.
 28. A method according to claim 26,wherein immediately after contact between said viscous petroleum andsaid treatment fluid formulation, said fluid flow path contains acomposition which includes 40 to 80 wt % of material derived from saidviscous petroleum and 20 to 60 wt % of material derived from saidtreatment fluid formulation.
 29. A method according to claim 28, whereinsaid polymeric material AA comprises polyvinylacetate which has been 60to 95% hydrolysed to polyvinylalcohol.
 30. A fluid flow path positionedat or downstream of a producing face of a subterranean formation,wherein said flow path contains a fluid comprising petroleum, water anda polymeric material AA which is a polyvinyl alcohol polymer orcopolymer which is not cross-linked, wherein said polymeric material AAcomprises polyvinyl acetate which has been 60-100% hydrolyzed topolyvinyl alcohol.
 31. A fluid flow path according to claim 30, saidfluid flow path containing a composition which includes 40 to 80 wt % ofmaterial derived from a viscous petroleum and 20 to 60 wt % of water.32. A method for reducing the viscosity of a viscous composition whichis arranged to flow along a fluid flow path, said method comprisingcontacting the viscous composition in said fluid flow path with atreatment fluid formulation, said treatment fluid formulation comprisinga polymeric material AA which includes —O— moieties pendent from apolymeric backbone thereof, wherein said polymeric material AA comprisespolyvinylacetate which has been 60 to 95% hydrolysed topolyvinylalcohol, wherein polymeric material AA is optionallycross-linked and wherein said treatment fluid formulation is initiallycontacted with said viscous composition in said fluid flow path at ordownstream of a producing face of a subterranean formation.